Method and apparatus for an automated plate handler with slip sheet removal mechanism

ABSTRACT

The primary function of the optional handler is to make plates available on demand to the imaging engine. A multitude of plates are stored inside cassettes and these cassettes are loaded into the handler. There may be up to four cassettes residing in the handler. Inside a cassette there may be a protective interleaf sheet, sometimes called a slip sheet, between each plate which is removed by the handler and discarded. The handler receives commands from the engine control sequencer which provides instructions as to what cassette needs to be accessed to make a plate available to the picker mechanism so the plate may be conveyed to the imaging engine. Conversely the handler provides status information to the engine to make full interaction with the system possible.

This application is a Continuation of application Ser. No. 08/693,740filed Aug. 7, 1996 now U.S. Pat. No. 5,655,452.

BACKGROUND OF THE INVENTION

Printing processes utilize a vast array of different technologies totransfer written content to various distribution media. Organizationsusing varying printing processes include modest-volume quick printers,book and financial publishers, newspaper companies, forms companies, allsizes of commercial printers (for advertising etc.), and, publicationprinters (for magazines and periodicals). These types of organizationshave a common process whereby information is transferred from someoriginal layout form to an intermediate aluminum or polyester platematerial which is then hung on a standard printing press to enablemultiple identical replication of that information on paper or somesimilar print media.

This process has typically been performed by optically creating apolyester film which contains the information, optically transferringthe information from the film to a plate material by use of a lighttransfer or contact to a light-sensitive chemical emulsion which isbonded to the plate, and then hanging the developed plate on a press inalignment (one for each color separation desired). The plates rotatealong with the press cylinder and alternately come in contact with inkrollers and then an intermediate transfer blanket. The ink which isaccepted by the transfer blanket then transfers the information to thepaper during rotational contact.

Recently the development of computer-to-plate, hereinafter C2P, systemsand processes have provided alternative printing options. The C2Pprocess eliminates the film as an intermediate transfer mechanism andallows the optical exposure of the plate directly. This reduces thenumber of steps required in the printing process of the information andpotentially reduces the cost related to the generation of theintermediate film and its handling. C2P systems more readily allow aprocess which creates plates for shorter-run printing (below around50,000 impressions).

In basic terms, a C2P system accepts input jobs/pages written in a pagedescription language, for example, POSTSCRIPT®. These jobs arecontrolled through execution by priority and scheduling workflowsoftware. Jobs are then sent through a raster image processor to aplatemaker for exposure. The data is being transformed throughout thisprocess. The platemaker engine takes this data and prints it on a metalsheet of aluminum which is later notched, bent, hung on the press, inkedand made ready to image paper. An imaging engine and process for imaginga plate is described in commonly owned U.S. Pat. No. 5,345,870, herebyincorporated by reference into the present application.

The inclusion of a C2P system into a printing operation suggests agreater extent of automation which can be achieved. A full C2P processcan automate, through the use of computers and special equipment, thetransfer of information from the original layout to the press plate. Assuch, C2P is not only an improvement in the specialized equipment butalso in the process which utilizes that equipment. Viewing C2P as aprocess includes a high level of workflow management to replace manualeffort with computer-driven effort with a goal to increase productivityand efficiency. Workflow encompasses such concepts as queue management,color calibration, revision control, press consumables control,inventory tracking, job and cost tracking, etc.

Also included in the automation of a C2P system is the media handling.It is necessary to supply plates individually from a plate supply areato the platemaker engine and it is desirable to reduce the amount ofoperator handling involved. Unexposed plates are normally supplied inpackages of 25 to 100 with interleaf sheets between the plates forprotecting the sensitive emulsion side of the plates, which is extremelysensitive to scratches. The stack of plates needs to be loaded into asupply area of a platemaker in a manner to keep the stack of platesaligned with automation mechanisms for removing a plate from the stack,and for discarding the interleaf sheet from the stack. These functionsare optimally performed within a covered light-tight environment toprevent unintentional exposure of the light sensitive plate surface. Theplatemaker engine requires plates of varying sizes and formats ondemand. It is beneficial to present a variety of plate sizes and formatsto an automated mechanism for selecting the plate needed by theplatemaker engine. It is important to be able to reload the plate supplyarea without interrupting the operation of the platemaker engine. Thesefunctions generally will maximize the output of the platemaker engine,by eliminating time which an operator would manually handle the platesand during which the platemaker engine might be interrupted.

Accordingly it is an object of the present invention to provide anautomated C2P system having a workflow software capable of controllingand sequencing the tasks performed by the C2P system from accepting ajob input to the system as POSTSCRIPT® and output the job from thesystem as exposed images on printing plates.

It is a further object of the invention to increase productivity andefficiency in a C2P system by providing automated queue management.

It is a specific object of the invention to automate the operation ofsupplying plates on demand from a plate storage area within a C2P systemto the platemaker engine.

It is a further object of the invention to provide a plate handlingmechanism to position a plurality of plate cassettes containing varyingplate sizes within the plate storage area, making a desired platecassette accessible to a plate picking mechanism.

It is another object of the present invention to automatically removeand discard the interleaf sheets from between plates after a plate isindividually removed from the stack of plates.

It is another object of the invention to automatically pick a plate fromthe top of a stack of plates and deliver the plate to the platemakerengine in a manner which accommodates a variety of plate sizes andformats.

SUMMARY OF THE INVENTION

A method for automatically selecting a plate for imaging in an automatedplate handler, comprises automatically positioning a plurality of stacksof plates stored in the plate handler to thereby place a stack of theplate size required for an imaging job in an access position. A singleplate is automatically separated and removed from the stack of plates inthe access position and then transferred out of the plate handler forimaging. A slip sheet is automatically removed from on top of the stackof plates in the access position.

An apparatus for automatically selecting a plate for imaging in anautomated plate handler has a first mechanism for automaticallypositioning a plurality of stacks of plates stored in the plate handler.The first mechanism places a stack of the plate size required for animaging job in an access position. A second mechanism is provided forautomatically separating and removing a single plate from the stack ofplates in the access position and then transferring the single plate outof the plate handler for imaging. Also a third mechanism forautomatically removing a slip sheet from on top of the stack of platesin the access position is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention will be better understood andfurther objects and advantages of the invention will become apparent inthe following detailed description of the invention, when taken with theaccompanying drawing(s), in which:

FIG. 1 is a schematic illustration of an electronic prepress systememploying a platesetter shown from a side view with a plate handler andplate picker mechanism according to the present invention;

FIG. 2 is a partial sectional front view of the plate handler viewed inFIG. 1;

FIG. 3 is an isometric view of an assembly portion of the plate handlershown in FIG. 2, particularly featuring an elevator mechanism and atable supporting mechanism according to the present invention;

FIG. 4 is a detailed isometric view of the plate picker mechanism shownin FIG. 1;

FIG. 5 is a simplified top view of the picker mechanism of FIG. 4positioned over a handler cassette within the plate handler according tothe present invention;

FIG. 6 is a side view of a portion of the plate handler showing theplate picker in the process of picking a plate from a cassette, and alsofeaturing a slip sheet removal mechanism according to the presentinvention;

FIG. 7 is an isometric view of a plate cassette used in the platehandler according to the present invention; and

FIG. 8 is a detailed side sectional view of a portion of a platecassette as shown in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

The computer to plate imaging system shown in FIG. 1 and generallyreferred to as reference number 10, is a complete system for plateproduction, where digital data files representing a publication (orprinted image) are input to the system 10, and plates ready to go on aprinting press are output from the system 10. Most of the operation ofthe system is automated, requiring a minimum of operator intervention.The system is comprised of a front-end server 12, a raster imageprocessor (RIP) 14 and a platemaker or platesetter 16. The front-end 12sends jobs to the platesetter 16. The platesetter 16 has three majorcomponents. An optional on-line plate handler 18, the imaging engine 20and an optional on-line plate processor/plate stacker 22. The platehandler 18, hereinafter handler, contains a supply of plate containersor cassettes 24. The handler can hold as little as two cassettes or asmany as three, four, or five depending on user requirements. Eachcassette is a light tight container that houses a stack of plates 26.The cassettes 24 can be vertically adjusted by the handler 18 to makeplates 26 stored within a particular cassette available to a plateshuttle mechanism 28, hereinafter referred to as the picker 28. Thepicker 28 removes a single plate from the selected cassette andtransports the plate between the handler 18 and the engine 20, whichwill be described in detail hereinafter.

The primary function of the handler 18 is to make plates 26 available ondemand to the imaging engine 20. A multitude of plates 26 are stacked ineach cassette 24 and the cassettes 24 are side-loaded into the handler18 by an operator. Between each plate in a stack there may be aprotective interleaf sheet or slip sheet which is removed by the handler18 and discarded by a slip sheet removal mechanism 25. The handler 18receives commands from the engine 20 by workflow software, whichprovides instructions to the handler 18 about what cassette 24 needs tobe accessed to make a plate available to the picker 28 so the plate maybe conveyed to the imaging engine 20. The handler 18 in turn providesstatus information to the engine 20 through the workflow software tomake full interaction with the system 10 possible.

The front-end 12 sends data to the engine 20 through an interfaceconnection. Typically this data represents a "job" which requires theimaging of plates. This data contains information about the job'srequirements, such as the type of plate, its size and plate thickness,the number of plates that are part of the same job, etc. The engine 20interfaces electrically with the handler 18 to exchange machinefunctional and operation data which is input into the workflow software.The handler 18, through the engine 20, sends data to the workflowsoftware from data stored in each loaded cassette 24 representing platesize and quantities available in the cassettes 24. The handler 18 hasthe capability of reading an ID tag on each cassette which has adescription of the plate type inside. This ID tag is in the form of abar-code or other means. If a required plate size is unavailable, theengine 20 notifies an operator through a platemaker control terminal 30,so the operator can load the needed cassette into the handler 18. Theengine 20 passes information to the handler 18 defining the next platesize or thickness required for imaging and which cassette 24 is to beplaced in the queue, or in the correct position for access by the picker28. The cassettes 24 store different sizes and/or thicknesses of plates26 so the handler 18 positions a specific cassette 24 so that the picker28 can access the required plate inside the specific cassette. Thehandler 18 insures the slip sheet, if present, has been removed from thesurface of the top plate with the slip sheet removal mechanism 25. Thepicker 28 then moves over the positioned cassette, the plate is"picked," and the picker 28 returns to the imaging engine (home)position to deliver the plate. The imaging engine 20 accepts the plateand while the picker is in the engine 20 in the home position, thehandler 18 is free to position the cassettes 24 in preparation for thenext plate to be imaged.

Referring to FIG. 2, some basic elements of the handler 18 are shown.The handler 18 has a support frame 32 which surrounds several tables 34,36. The lowermost table 36 is attached to and supported by a brace 38 onthe underside of the lowermost table 36. The brace 38 is attached to anelevator mechanism, referred to generally as 40 and to be describedhereinafter, which raises and lowers the brace 38 and the lowermosttable 36 supported by the brace 38. The upper three tables 34 positionedabove the lowermost table 36 rest upon the lower table 36 on tablespacers 42 which are secured to the outer ends of the undersides of theupper three tables 34. In FIG. 2, the upper three tables 34 are shownbeing supported by a table support mechanism, referred to generally as44 and to be described hereinafter, which separates the tables to allowclearance space for the picker to enter into above the cassette fromwhich a plate is going to be picked. When the table support mechanism 44is inactive, the table spacers 42 contact the table immediately belowthe table which the spacers are attached to, in a manner so as tosupport that table. The tables 34, 36 can be positioned by the elevatormechanism 40 as a group, with the three upper tables 34 resting on thelowermost table 36 on the brace 38 of the elevator mechanism 40.

Referring additionally to FIG. 3, the support frame 32 has four verticalsupport beams 46 provided with guide tracks 48 for guiding the tableswhile being raised or lowered. Each table has four rotatable guidewheels 50 (only two shown as viewed in FIG. 2) which ride in the guidetracks 48 at the corners of each table. The table support mechanism 44comprises four vertical shafts 52 with bearing mounts 54 at the upperends of each shaft 52. The shafts 52 are rotatable relative to thebearing mounts 54 which are attached to the topside of the support frame32. The support frame 32 has bores (not shown) which the shafts passthrough to extend downward to the tables 34, 36. At the lower ends ofthe shafts 52 are support bars 56 which protrude horizontally outwardfrom the shaft 52 at a right angle therefrom, and lower bearing mounts58 attached to the four vertical support beams 46. In an inactiveposition, the support bars 56 face outward and away from the tables, asshown in FIG. 3. A linkage 60 connecting the shafts 52 transmits rotarymotion from a drive motor 62 to rotary plates 64 fixed to the tops ofeach shaft 52 and to the shaft of the drive motor 62. Upon apredetermined rotation by the drive motor 62, the linkage 60 connectingthe rotary plates causes the four shafts 52 to rotate 90 degrees,positioning the horizontal support bars 56 facing inward toward thetables, in the active position as in FIG. 2. The support bars 56 are inposition to support the tables 34 above the cassette 24 to be accessedby the picker 28.

The elevator mechanism 40 comprises a chain drive system having fourchain drives 66, one mounted on each support beam 46. Two rotatablesprockets 68, 70 are mounted on each support beam 46 in an upper andlower position to cooperate with the chains 66 and transmit rotarymotion of the sprockets 68, 70 into linear motion of the chains 66. Thelower sprockets 70 are attached to two horizontal shafts 72 whichtransmit rotary motion from a main drive shaft 74 through several gearboxes 76 and couplings 78. The main drive shaft 74 is powered by a drivemotor 80 through a belt 82 and pulley 84 connection.

The brace 38 is connected to the chains 66 on the inner sides of thesupport beams 46 so that upon rotation of the drive motor 80, the chaindrive system raises or lowers the brace 38, the lowermost table 36, andany upper tables 34 resting thereon which are not supported by the tablesupport mechanism 44 at the time.

Referring now to FIG. 4, the picker 28 is shown supported on parallelrails 90 which are fixed to the interior of the engine compartment 20(FIG. 1). Complementary rails 92 are mounted inside of the handler 18 asshown cross section in FIG. 2 and isometrically in FIG. 3, allowing thepicker to move smoothly between the engine 20 and handler 18. The rails92 inside the handler are secured to the support beams 46 of the handlerframe 32. The picker 28 has a carriage 94 which is supported on therails (90 or 92 depending on whether the handler is in the engine or thehandler respectively) by three guide wheels 96 which engage the rails 90(or 92) on each side of the carriage 94. Also two friction wheels 98engage the rails 90 (or 92). The friction wheels 98 are driven by amotor 100 mounted on the carriage 94 through a connection to a driveshaft 102 and a belt and pulley mechanism 104 on each side of thecarriage 94. The motor 100 operates in two directions to effectivelypropel the picker carriage 94 in forward and reverse from the enginecompartment 20 to the handler 18. The carriage 94 supports three rows106, 108, 110 of suction cups and an associated vacuum manifold 112 andvacuum tubing (not shown) between the manifold 112 and the three rows106, 108, 100 of suction cups. The suction cups 114 are mounted onspring loaded fittings 116 to allow compression of the suction cups 114against a plate during picking to ensure attachment of the plate to thepicker 28. The first row 106 of suctions cups that extends the furthestinto the handler 18 is pivotable with respect to the carriage 94. Aneccentric drive 118 and linkage 120 pivots the first row 106 of suctioncups in a "peeling" motion. The eccentric 118 is driven by a motor 122mounted on the carriage 94 to break or peel the edge of the plate beingpicked away from the stack. The middle row 108 of suction cups remainsfixed with respect to the picker carriage 94. The third row 110 ofsuction cups slides out from the middle row 108 of suction cups. Tworails 124, 126 are mounted for sliding through complementary bearings(not shown) in the carriage body 94 on the both sides of the picker 28.On the right side of the picker viewed in FIG. 4, the rail 126 has afriction drive wheel (not shown) in driving contact with the rail 126.The drive wheel is driven by a drive motor 128 through a belt and pulleymechanism (not shown), all of which are mounted to the carriage body 94so as to transmit rotary motion of the drive wheel into linear motion ofthe rails 126, 124 relative to the carriage body 94. The third row 110of suction cups being movable relative to the other rows 106, 108 ofsuction cups expands the overall size of the picker 28 and the coveragearea of the suction cups 114 to accommodate for various sized plates.

FIG. 5 illustrates a simplified top view of the picker 28 positionedover a cassette 24 in the handler. The first row 106 of suction cups 114is positioned near an inner edge 130 of the cassette 24 against whichthe plates are referenced regardless of the plate size. Four differentplates having different sizes are depicted by dashed lines and areindicated as plates A, B, C, and D. Plate A is the smallest plate andthe middle row 108 of suction cups of the picker 28 is positioned nearthe opposite edge 132 of plate A from the reference edge 130. The middlerow 108 has a fixed position relative to the first row 106 (exceptingthat the first row is pivotable) to pick up plate A without the use ofthe third row 110 of suction cups. The third row 110 is shown in anextended position by solid lines, at the far edge 134 of the largestplate D opposite from the reference edge 130. The third row 110 ofsuction cups is also shown by dashed lines in a non-extended position.The third row 110 of suction cups is used to expand the size of thepicker 28 to cover the areas for various size plates, such as B, C, andD, larger than the smallest plate A and smaller than or equal to thelargest plate D, as indicated by arrow 136. Arrow 138 shows the relativemovement of the picker 28 including all three rows 106, 108, 110 ofsuction cups 114 with respect to the handler cassette 24 and the engine.

Referring now to FIG. 6, the slip sheet removal mechanism is generallyindicated as 25. The mechanism 25 is for the purpose of preventing aslip sheet 140 from sticking to the bottom of a plate 142 which isattached to the picker 28, securing the slip sheet 140 on the top of thestack of plates in a cassette 24 to the slip sheet removal mechanism 25,and subsequently completely removing the slip sheet 140 from the stackof plates in the cassette 24. The mechanism 25 comprises a plurality ofsuction tubes 144 mounted on a first pivotable shaft 146, an optionalpeeler air blast 148, a plurality of fingers 150 mounted on a secondpivoting shaft 152, a plurality of nip wheels 154 mounted on a thirdpivoting shaft 156 (only one of each seen in drawing due to side view),and a rotatably driven roller 158 positioned below the nip wheels 154which are in rolling contact during part of the slip sheet removalprocess, to be described hereinafter. The suction tubes 144 are fixed tothe pivoting shaft 146 to pivot upon being driven by motor 160 through adrive belt and pulley connection 162. The fingers 150 are fixed topivoting shaft 152 which is driven by a similar drive connection to amotor (not shown). The nip wheels 154 are each mounted to an extensionarm 164 which is attached to a bracket 166 mounted on the pivoting shaft156. The extension arm 164 is spring loaded at the connection to thebracket to allow for the extension arm 164 to pivot or give slightlywhile pressure is applied between the nip wheel 154 and the roller 158.The shaft 156 is rotated in forward and reverse by the drive motor 168through a drive belt and pulley connection 170. The roller 158 is drivenby a motor 172 also through a belt and pulley connection 174. It will beunderstood by those skilled in the art that equivalent means forrotating the pivoting shafts 146, 152, 154, and rotating roller 158, maybe substituted therefor without departing from the spirit of theinvention. The driven shafts and motors for driving the shafts are allmounted to a mounting bracket 176 which is connected to the supportbeams 46 of the handler 18. Operation of the slip sheet removalmechanism 25 will be described hereinafter.

Referring now to FIG. 7 and FIG. 8, a cassette 24 for loading into theplate handler is shown. The cassette has a removable cover 180, which isremoved and replaced in a vertical direction relative to a rectangularbottom container 182 as indicated by arrows. The bottom container 182comprises a base plate 184 surrounded by four aluminum side extrusions186. The extrusions 186 are attached at the four 90 degree corners byspring clips and adhesive (not shown). The base plate 184 is containedwithin a slot 188 in the edge of each extrusion 186 and is held in placewith an adhesive on the top side 190 of the base plate 184 and a pieceof continuous round flexible urethane belting 192 on the bottom side ofthe base plate 184. The round belting 192 is retained in a thin groove194 provided in the extrusion 186.

Three channels 196 (one shown) are fastened to the bottom side of thebase plate 184. The channels 196 act as reinforcing stiffeners for thebottom container 182, and also are housings for three locator bars 198.Each locator bar 198 is attached within a channel 196 by an adhesive. Anadjustable stop 200 is provided on each locator bar 198 to slide alongthe locator bar and be fastened to a set position by a lock screw 202which screws into holes 204 drilled into the locator bars 198. The threeadjustable stops 200 locate and secure a stack of plates 26 againstseveral reference blocks 206 fastened to the side extrusions 186. Theadjustable stops 200 allow multiple sizes of plates 26 to be heldagainst the reference blocks 206 within a single bottom container 182.The base plate 184 is provided with embossed areas 208 for the referenceblocks 206 to be set within, which prevents the plates referencedagainst the reference blocks 206 from sliding between the referenceblock 206 and the base plate 184 and maintaining alignment of the plateswith respect to the reference block 206.

The cover 180 comprises a top plate 210 and four side extrusions 212surrounding the top plate 210. The extrusions 212 are fastened togetherat the four corners of the top plate 210 by spring clips and adhesive(not shown). The top plate is secured to a ledge portion 214 of theextrusions 212 by an adhesive. Two of the four side extrusions have ahandle portion 216 formed in the extrusion 212 which cooperate withhooks on the undersides of the cassette tables in the handler to removeand replace the cassette cover (to be described hereinafter). The insideof the top plate 210 has a layer of foam 218 attached, to ensure thatthe plates on the top of a full stack of plates 26 do not slide over thetops of the reference blocks 206 during loading of a cassette 24 intothe handler 18. The cover 180 and the bottom container 182 areconstructed from light proof materials, so that when the plates areenclosed within a covered cassette, there is no exposure of the lightsensitive plate contained within the cassette. The attachment areabetween the bottom extrusions 186 and the cover extrusions 212 hasmagnetic strips 220 which ensure the cover 180 is attached securely tothe bottom container 182 and that no light will enter the cassette 24during handling.

The side extrusions 186 are provided with a beveled portion 230 whichaid in the loading of the cassette 24 into the plate handler 18. Thehandler 18 has a loading platform 232 shown in FIG. 2, extendinghorizontally from the vertical beams 46 of the handler. The loadingplatform 232 has rows of grooved wheels 234 mounted for rotation withinthe loading platform 232. The grooved wheels 234 cooperate with thebeveled portion 230 of the side extrusions 186 of the cassette 24 duringloading and serve to register the cassettes in a reference positionwithin the handler. All tables 34 and 36 within the handler are alsoprovided with the rows of grooved wheels to facilitate smooth and easyloading of the cassette from the loading platform onto the supporttables in the handler, while maintaining the cassette in register. Thebeveled portions 230 cooperate with the V-grooved surface 236 of thegrooved wheels 234 on opposite outer sides of the cassette 24 for properalignment. The cassette is designed to align the plates inside thecassette against the reference blocks provided on the interior of thecassette, and also register the cassette into a reference positionwithin the handler, as shown in FIG. 5, regardless of the plate sizecontained in the cassette. The parallel rails 92 in the handler arefixed relative to the wheels of the selected table in the accessposition. This ensures the registration of the plates within thecassette relative to the rails 92, and the registration is transferredto the complementary rails 90 in the engine compartment, and thereby theplate is delivered in register into the engine from the handler.

Additional locator stops 238 are provided on each table to assist inregistering the cassette 24 in the loading direction so that thecassette 24 is pushed into the handler 18 along the grooved wheels 234of the table 36, but only to a predetermined location so that thecassette 24 is registered with respect to two dimensions and to thepicker rails 92. These additional locator stops 238 are spring loadedand are located between the grooved wheels 234 within each row ofgrooved wheels on a table 36. The stops 238 contact an underside 240 ofthe side extrusions 186 while the cassette 24 is being loaded, and whenthe stop 238 comes into contact with a recess (not shown) formed in theunderside of the extrusion, the spring force behind the stop 238 forcesthe stop into the recess and locks the cassette 24 at the predeterminedlocation on the table. The wheels 234 register the cassette with respectto the two reference blocks 206 on one side of the cassette, while thelocator stops 238 within the rows of the wheels 234 register thecassette 24 with respect to the third, alone reference block 206 on theneighboring side of the cassette. Then the plates are registered in aknown location relative to the picker, as depicted in FIG. 5.

The loading platform can be incorporated into the design of the doorsand covers for enclosing the handler in a light tight environment. Theloading platform can function both as a door into the cassette loadingarea, and as the loading platform. This is accomplished by providing anattachment hinge on the handler frame for the loading table to pivotbetween the two functional positions. The loading table is pivoted upfor a closed door position, and down and horizontally as shown in thefigure for an open, cassette loading position.

Cassettes loaded into the handler house the plates. At any one time, acassette holds only like plates (same type, gauge, size, etc.).Typically, there is a maximum of 50 plates of 0.012" gauge, 75 plates of0.008" gauge, or 100 plates of 0.006" gauge, in a single cassette. Thereare several distinct cassette sizes. A cassette of a specific size holdsa range of plate sizes inside, however only one size plate is loadedinto a cassette at any one time. Fillers or guides are used to take-upthe space between plate and cassette boundaries. The reference positionof the plates within the cassette is described above with reference toFIG. 5. Packaging of plates within a cassette is related to both handleroperation and cassette transportability. There may be a mix of cassettesin the handler (two, three or four cassettes). All cassettes can bedifferent from each other, in that each houses a distinct set of platecharacteristics (type, size, gauge, etc.) There may be instances wheresome or all cassettes inside the handler have the same platecharacteristics.

Now, with reference to all the Figures, the method for using the platehandler 18 and picker 28 will be described. The primary function of thehandler 18 is to position a required plate on demand in an accessposition for the picker 28, which picks and delivers the required plateto the engine 20. Once the handler 18 receives a request from the engine20 for a specific plate, the following actions take place in thehandler, in cooperation with the engine 20. The picker 28 begins in thehome position within the engine 20. The slip sheet removal mechanism 25is positioned with the suction tubes 144, fingers 150, and nip wheels154 retracted (as shown in dotted lines for the suction tubes and nipwheels in FIG. 6) to clear the path of the tables 34, 36 forrepositioning by the elevator mechanism 40. The elevator mechanism 40moves the brace 38, lower table 36, and upper tables 34 supportedthereon, if any, to a cover removal/replacement position. In the coverremoval/replacement position, the selected table 36 is located directlybelow the table 34 supported by the support bars 56 of the table supportmechanism 44. Hooks on the bottom of the supported table 34 engage thecover 180 of the selected cassette 24 for either removal or replacement,so that the cover 180 is separated from or rejoined with the selectedcassette 24.

In FIG. 2, the cover removal/replacement position for the lower table 36is at a position where the open cassette 24 on the lower table 36contacts the cover 180 supported by the table 34 immediately above thelower table 36 held by the support bars 56. When the selected cassette36 is in the cover removal/replacement position, the upper tables 34 areall then supported by the brace 38. Then the support bars 56 and shafts52 are turned 90 degrees by means of the linkage 60 and drive motor 64.Once the support bars 56 are retracted from the path of motion of thetables 34, 36, the elevator mechanism 40 moves to the coverremoval/replacement position for the next selected table and cassette.The table support mechanism 44 moves the support bars 56 into thesupporting position underneath the table directly above the selectedcassette 24. The elevator mechanism 40 then moves the selected tabledown thereby separating the cover 180 of the selected cassette 24 fromthe selected cassette 24 so that the picker can access the plates 26contained within the cassette 24.

The picker 28 is then moved from the home position in the engine 20 intothe handler 18 along the rails 90 and 92. Depending on the size of theplate in the selected cassette 24 the picker 28 adjusts the third row110 of suction cups relative to the middle row 108 of suction cups toaccommodate for various plate sizes, if necessary (FIG. 5). The elevatormechanism 40 moves the selected cassette 24 and plates therein upward tocome into contact with the suction cups 114 on the picker 28 (FIGS. 4and 6). The suction cups 114 retract into the spring loaded fittings 116to accommodate for variations in the stack height of the plates 26 inthe cassettes 24, as the elevator 40 moves the cassette 24 up to thepicking position which is at a set vertical height relative to thepicker rails 90, 92. Therefore for a maximum stack height of a fullstack of plates, the suction cups 114 compress against the spring loadedfittings 116 and retract a length into the fittings, and for a depletedstack of plates, the suction cups 114 compress against the spring loadedfittings and retract substantially the same length minus the height ofthe stack depletion. The spring loaded fittings 116 also ensure that theplate and the suction cups 114 make contact to secure the plate onto thepicker 28. After the plate is attached to the picker 28 by the vacuumsuction, the first row 106 of suction cups on the picker 28 is pivotedupward, peeling back the edge of the plate 142 and creating a gapbetween the plate 142 and the slip sheet 140 underneath.

The slip sheet removal mechanism 25 activates the peeler air flow 148,and the fingers 150 are pivoted into position to hold down the edge ofthe slip sheet 140 while the elevator mechanism 40 lowers the cassette24 to a slip sheet removal position. The peeler air blast 148 remains onwhile the cassette 24 moves downward to separate the slip sheet 140 fromthe bottom of the plate 142 being picked by the picker 28, which maystick to the plate due to electrostatic charge. The fingers 150 arepivoted away from the slip sheet 140 and the suction tubes 144 arepivoted into position above the slip sheet edge. The suction cups on theends of the suction tubes are compliant and flexible so that when thevacuum is applied and contact is made between a suction cup and the slipsheet, the slip sheet material is drawn into the suction cup and theseparation of the slip sheet from the plate below it is initiated. Thecompliant suction cup deforms to break the slip sheet away from thelower plate as typically an attractive force exists between the slipsheet and the plate. This is also an important step in the process ofremoving the slip sheet because the slip sheet may be a porous materialand the vacuum applied through the suction tubes can pass through theslip sheet material and be applied to the plate below, which isundesirable when attempting to remove the slip sheet. The selectedcassette 24 is elevated to bring the slip sheet 140 into contact withthe suction tubes 144 while the vacuum is on. The suction tubes 144pivot upward slightly to break the adhesion of the slip sheet 140 to theplate below. The elevator 40 then moves the selected cassette 24downward from the slip sheet removal mechanism 25 and the suction tubes144 pivot back downward to the roller 158 with the slip sheet 140attached. The vacuum for the suction tubes 144 is turned off and theslip sheet 140 is released to the rotating roller 158 to pull the slipsheet 140 away from the stack. The nip wheels 154 pivot from theposition shown in solid lines to the position shown in dotted lines tocooperate with the roller 158 and remove the slip sheet 140. A sensor(not shown) indicates that the removal of the slip sheet 140 iscompleted and the rotating roller 158 is then halted. Meanwhile thepicker 28 lowers the first row 106 of suction cups from the peelingposition, and the picker 28 travels back into the engine 20 to the homeposition. For the next plate to be selected by the picker 28, the stepsare partially repeated if the same cassette 24 is being picked from, orthe steps are repeated from the beginning of the sequence for anothercassette.

In order to load cassettes into the handler, the following method stepsoccur in conjunction with the plate handler apparatus and the workflowsoftware as described previously. The handler has sensors positionedappropriately (not shown) to monitor the level of the plates containedin each cassette. Additionally the handler has the capability of knowingthe types of plates available so that when a plate needed by the engineis not available, or upon a sensor detecting an empty cassette, a signalis communicated to the engine and the operator is alerted through theoperator control terminal 30.

The picker 28 is returned (if not already there) to begin in the homeposition within the engine 20. The slip sheet removal mechanism 25 ispositioned with the suction tubes 144, fingers 150, and nip wheels 154retracted (as shown in dotted lines for the suction tubes and nip wheelsin FIG. 6) to clear the path of the tables 34, 36 for repositioning bythe elevator mechanism 40. The elevator mechanism 40 moves the brace 38,lower table 36, and upper tables 34 supported thereon, if any, to thecover removal/replacement position previously described. Then thesupport bars 56 and shafts 52 are turned 90 degrees by means of thelinkage 60 and drive motor 64. Once the support bars 56 are retractedfrom the path of motion of the tables 34, 36, the elevator mechanism 40moves to the cassette loading position for the selected table andcassette needing replacement. The cassette loading position is locatedwhere the selected table is adjacent to the loading platform 232 shownin FIG. 2 extending out from the handler 18 to support the cassette 24to slide horizontally between the selected table and the loadingplatform 232 during loading and unloading. Covers and door (not shown)are provided to enclose the entire handler frame to maintain thecassette in a light tight environment. The doors are provided to accessthe interior of the handler and at this time the door locks are releasedto allow operator access. Then the empty cassette is removed by slidingthe cassette out horizontally along the path formed by the groovedwheels in the selected table and the loading platform, and then thecassette is either reloaded or replaced with another cassette. Thecassette presence is monitored by sensors. After detecting the cassetteon the selected table, the handler waits for the doors to be closed andthen the door locks are activated. The elevator moves up to the coverremoval/replacement position for the selected cassette and normaloperation is resumed.

It will be understood that the preferred embodiment of the systemdescribed herein being a platesetter for imaging aluminum plates, can beused also with polyester plates, can be modified to perform as aproofing device rather than a platesetter, such as in commonly owned,pending U.S. application Ser. No. 08/496,714, entitled "ElectronicPrepress System With Multi-Function Thermal Imaging Apparatus," herebyincorporated by reference. Additionally the apparatus described hereinis applicable to production of thermally recorded printing plates aswell as photosensitive lithographic printing plates recorded by lightexposure, with various modification to the system's processing andimaging components, as appreciated by those familiar with the art.

While this invention has been described in terms of various preferredembodiments, those skilled in the art will appreciate that variousmodifications, substitutions, omissions and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims, including equivalents thereof.

We claim:
 1. A method for automatically selecting a plate for imaging inan automated plate handler, comprising the steps of:a. automaticallypositioning a plurality of stacks of plates stored in the plate handlerand placing a stack of the plate size required for an imaging job in anaccess position; and b. automatically separating and removing a singleplate from the stack of plates in the access position and transferringthe single plate out of the plate handler for imaging.
 2. The methodaccording to claim 1, wherein the stacks of plates stored in the platehandler are positioned substantially horizontally.
 3. The methodaccording to claim 1, wherein the step of positioning said plurality ofstacks of plates is performed by moving said plates substantiallyvertically.
 4. The method according to claim 1, wherein the step oftransferring the single plate out of the plate handler is performed bytransferring said plate substantially horizontally.
 5. The methodaccording to claim 1, wherein at least one of the plurality of stacks ofplates is a different size than at least one other of the plurality ofstacks of plates.
 6. An apparatus for automatically selecting a platefor imaging in an automated plate handler, comprising:an elevatormechanism for positioning a plurality of stacks of plates stored in theplate handler in an access position; a support mechanism for selectingone of said plurality of stacks of plates; and a shuttle mechanism forremoving a single plate from said selected stack of plates in the accessposition and transferring said plate out of the plate handler forimaging.
 7. The apparatus according to claim 6, wherein said stack ofplates stored in the plate handler are positioned substantiallyhorizontally.
 8. The apparatus according to claim 6, wherein said stackof plates move substantially vertically.
 9. The apparatus according toclaim 6, wherein said single plate is transferred out of the platehandler substantially horizontally.
 10. An apparatus for automaticallyselecting a plate for imaging in an automated plate handler and forremoving a slip sheet from the plate handler, comprising at least onesuction tube mounted on a first pivoting shaft mounted for rotation in abracket secured to the plate handler, said suction tube for attaching toa slip sheet on the top of a stack of plates and completely removing theslip sheet from the stack of plates.
 11. The apparatus according toclaim 10, further comprising at least one finger member mounted on asecond pivoting shaft mounted for rotation in the bracket, said fingermember holding down the slip sheet to the stack of plates in a holdingposition and allowing the suction tube to lift and remove the slip sheetfrom the stack of plates.